Sarcoidosis is a systemic inflammatory disease of unknown etiology which has no cure. It is thought to be caused by an abnormal Th1-type immune response to either a self or non-self antigen. However, how this aberrant immune response is initiated or perpetuated remains unknown. Also, current treatment approaches (e.g. corticosteroids) are non-specific, have toxicities, and may not halt disease progression. Invariant natural killer T (iNKT) cells are a unique immunoregulatory T cell subset believed to bridge the innate and adaptive immune systems. iNKT cells can dictate the Th1 vs Th2 nature of an immune response, an effect which may be mediated by specific subsets of CD4 and CD8 iNKT cells. In our RO3- funded study, we found that sarcoidosis subjects 1) had lower frequencies of circulating iNKT cells compared to controls which correlated with disease severity, 2) had skewed circulating subsets of iNTK cells with lower frequencies of the CD4-CD8- subset compared to controls, and 3) had higher percentages of CD56+ iNKT cells which correlated with the degree of airway obstruction. We also provide novel data showing IL-17 production by human iNKT cells, supporting the emerging concept from mouse studies that iNKT cells may modify Th17 in addition to Th1/Th2 responses. Specific Aims. Based on our preliminary data, we hypothesize that Th1 and Th17-type inflammation in sarcoidosis is promoted by "activated" CD4-CD8- iNKT cells which selectively leave the circulation and home to the lung. These "activated" CD4-CD8- iNKT cells express CD56. To test these hypotheses, we will determine 1) how iNKT cell subsets and effector function in the blood and lung relate to disease severity and phenotype, 2) how the subset composition and effector function of iNKT cells at baseline and over time predict disease progression and 3) the phenotype, effector functions, and differentiation potential of CD56+ vs CD56- iNKT cells. Experimental Approach. We will apply new flow cytometric panels for iNKT cell identification, and novel optimized assays to detect a diverse range of effector functions from individual iNKT cells ex vivo to measure the numbers, subsets and effector function of iNKT cells in the blood and lung of sarcoidosis subjects and controls at baseline and longitudinally and relate these findings to measures of disease severity, progression and phenotype. Finally, we will determine the phenotypic and functional properties of CD56+ iNKT cells from controls and sarcoidosis subjects and the differentiation potential of CD56- iNKT cells in vitro. Significance of the results. Our data relating iNKT subsets, effector function and activation markers to disease phenotype and severity in sarcoidosis suggest that these cells play a role in the initiation or persistence of granulomatous inflammation. Accomplishing these Aims will provide knowledge about how iNKT cells might be targeted for novel therapeutics, how CD56, which has no mouse homologue, might serve as a marker of disease phenotype or severity, and how human iNKT cells might contribute to inflammatory responses in other human diseases. PUBLIC HEALTH RELEVANCE: The overarching goal of the patient-centered research project for which we are seeking support from the NIH is to comprehensively study the biology of a recently identified immunoregulatory T cell, the natural killer T cell, in patients with sarcoidosis. Among the objectives of this project are to identify whether this T cell could be a new target for the development of more specific therapies, and whether the function of this T cell could serve as a predictor of which patients will have progressive lung disease. Accomplishing the proposed studies, which will advance the knowledge about the immunology of sarcoidosis, may someday help reduce suffering of patients with sarcoidosis and thereby promote lung health and improve patients'lives and possibly help prevent this lung disease.